Astrostatistics, and Brown Dwarfs

Chris Koen, Dept. Statistics, University of the Western Cape

The GMC mass distribution in M33, as determined from radio flux measurements

HartRAO observations of G12.89+0.49

HartRAO observations of G12.89+0.49: detail

What are brown dwarfs?

• Stars : stable fusion of Hydrogen, M>70

• Planets: no nuclear reactions, M<13

• Intermediate objects with can sustain burning of Deuterium

JM

JM

JJ MMM 7013

A few properties

• Radius ~ 0.1 R₀• Surface temperature < 3000 K• Luminosity ~ 10⁻⁴ L₀• Central temperature ~ 10⁶ K• Deuterium burning lifetime a few Myr• Spectral classes M, L, T

A conventional Hertzsprung-Russell diagram

The ultracool bottom end of the HR diagram

The Sun; M, L, T dwarfs; the planet Jupiter

• “Only a few hundred stellar radio sources are now known” (SKA website).

• Because of their low temperatures and small radii, radiation levels of brown dwarfs are lower than those of stars.

• Nonetheless, radio emission has been detected from a few late M (i.e. spectral types M7-M9) and L dwarfs.

• The emission is non-thermal, i.e. it is due to the action of magnetic fields.

What do astronomers hope to learn from the radio emission of brown dwarfs?

• Only direct access to magnetic fields

• Field configuration

Extent of the study to data

• About 90 objects have been studied (more than 500 L and T dwarfs known)

• Only 9 detections• Quiescent , flaring and burst emission have

been seen• Quiescent emission not always at the same

level • Mostly single frequency

Quiescent radio emission from UCDs Name Spectral type Flux (microJy)

LHS3003 M7 270±40 2M1048-3956 M8 140±40 TVLM513-46 M8.5 190±15 LSR1835+3259 M8.5 525±15 LP944-20 M9 74±13 BRI0021-0214 M9.5 83±182M0746+2000 L0.5 286±24 2M0523-1403 L2.5 231±14 2M0036+1821 L3.5 134±16

Flaring radio emission from UCDs Name Spectral type Flux (microJy)

2M1048-3956 M8 (29.6±1)X10⁴ TVLM513-46 M8.5 980±40 LP944-20 M9 2600±2002M0036+1821 L3.5 720±40

DENIS 1048-3956 flaring emission at 4.80(gray) and 8.64 GHz (black)

8.44 GHz observations of TVLM 513-46546

8.44 GHz observations of 2M0036+2000

Acknowledgments

Comparison of the sun, MLT dwarfs, and Jupiter: Dr. Robert Hurt of the Infrared Processing and Analysis Center

First HR diagram: WikipediaSecond HR diagram : Space Telescope Science Institute

Maser data: Dr. Sharmila GoedhartTVLM 513-46546: Hallinan et al. (ApJ 663, L25; 2007)2M0036+2000: Hallinan et al. (ApJ 684, 644; 2008)

Denis 1048-3956: Burgasser & Putman (ApJ 626, 486; 2005)